Nanocrystal Dots Research Articles

Fabrication of nano battery from CdS quantum dots and organic polymer

Efficient energy storage systems are recharged from the nano batteries; however, the available energy of present nanomaterial batteries remains capable for many applications due to the limited basic charging capacity of the electrode materials. A cadmium sulfide (CdS) nanocrystal (NCs) or quantum dots (QDs) that was prepared by chemical reaction and were fabricated nano battery device using the PVV / Li: graphite / CdS / Al. The optical properties of the CdS QDs were described by the spectrometers of ultraviolet-visible (UV-Vis.) and photoluminescence (PL), the results are indicating that the CdS QDs prepared where nanocrystalline structures are formed. The energy gap (Eg) of CdS QDs measured from PL was found to be about 2.69 eV. The CdS QDs led to improving the performs of the nano battery in terms of enhancing the mobility of the carrier's charging and consequently the processes of recombination between CdS QDs and Li-ions. The characteristics of the current-voltage (I-V) indicate acceptable conditions for the generation of light at (3 Volt). The structures can be designed to determine the fundamentals of ion and electron transport for energy storage in nanostructures and to test the limits of three-dimensional nano battery technologies. The nano battery device from semiconductor substance (CdS QDs) with (Li) has been successful in operating the nano battery with a few voltages giving a good current. Fabrication of CdS QDs and Li nano battery devices was involved in enhancing the efficiency of the nano battery devices.

Spin-Controlled Charge-Recombination Pathways across the Inorganic/Organic Interface.

Charge transfer and recombination across the inorganic/organic interface in nanocrystal or quantum dot (QD)-molecule hybrid materials have been extensively studied. Principles of controlling charge transfer and recombination via energetics and electronic coupling have been established. However, the use of electron spin to control transfer and recombination pathways in such systems remains relatively underexplored. Here we use CdS QD-alizarin (AZ) as a model system to demonstrate this principle. Using time-resolved spectroscopy, we found that the charge-separated states (QD--AZ+) created by selectively exciting AZ molecules mostly recombined to regenerate ground-state complexes, whereas apparently the "same" charge separated states created by exciting QDs recombined to produce AZ molecular triplet states. Such a difference can be traced to the distinct spin configurations between excited QDs (QD*, with an ill-defined spin) and AZ (1AZ*, spin singlet) and the asymmetric electron and hole spin-flip rates in II-VI group QDs. The transferability of such a principle was confirmed by similar observations obtained for CdS QD-tetracene complexes. Opening an avenue for controlling charge transfer and recombination pathways via electron spin is potentially important for applications such as artificial photosynthesis.

Light–Matter Interaction of Single Quantum Emitters with Dielectric Nanostructures

Single quantum emitters are critical components for many future quantum information technologies. Novel active material systems have been developed and transitioned into engineering efforts at nanoscale. Here, we review recent progress of diverse quantum emitters and their optical properties, including fluorescent point defect in bulk and single nanocrystal, two-dimensional materials, and quantum dots (QDs). Remarkable progress has also been made in controlling spontaneous emission by utilizing the local density of optical states in dielectric photonic nanostructures. We focus on the enhanced light–matter interaction between the emitter and cavity, enabling the realization of efficient and fast single photon sources.

REFRACTIVE INDEX NANOSENSOR USING PLASMONIC ENHANCEMENT OF PHOTOLUMINESCENCE

A refractive index nanosensor is proposed on the basis of plasmonic enhancement of quantum dot (nanocrystal) photoluminescence in the presence of a metal nanoparticle. Calculations of a silver elongated spheroid in the liquid show that the changes in the sensitivity of such a nanosensor to a refractive index can be of the order of 10 –4 provided that the photoluminescence intensity detection is of the order of 1 %.

From Large-Scale Synthesis to Lighting Device Applications of Ternary I-III-VI Semiconductor Nanocrystals: Inspiring Greener Material Emitters.

Quantum dots with fabulous size-dependent and color-tunable emissions remained as one of the most exciting inventories in nanomaterials for the last 3 decades. Even though a large number of such dot nanocrystals were developed, CdSe still remained as unbeatable and highly trusted lighting nanocrystals. Beyond these, the ternary I-III-VI family of nanocrystals emerged as the most widely accepted greener materials with efficient emissions tunable in visible as well as NIR spectral windows. These bring the high possibility of their implementation as lighting materials acceptable to the community and also to the environment. Keeping these in mind, in this Perspective, the latest developments of ternary I-III-VI nanocrystals from their large-scale synthesis to device applications are presented. Incorporating ZnS, tuning the composition, mixing with other nanocrystals, and doping with Mn ions, light-emitting devices of single color as well as for generating white light emissions are also discussed. In addition, the future prospects of these materials in lighting applications are also proposed.

Dialectics of nature: Temporal and spatial regulation in material sciences

The cooperative interaction distance measure has been proposed as a novel law pertaining to dialectics of nature, and has been extensively carried out in the design of functional nanomaterials. However, the temporal and spatial dimensions are akin to yin and yang, and thus temporal regulation needs to be accounted for when implementing the above-mentioned principle. Here, we summarize recent advances in temporally and spatially regulated materials and devices. We showcase the temporal regulation of organic semiconductors for organic photovoltaics (OPVs) using the example of exciton lifetime manipulation. As an example of spatial regulation, we consider the distribution of charge carriers in core–shell quantum dot (QD) nanocrystals for modulating their optical properties. Long exciton lifetime can in principle increase the exciton diffussion length, which is desiable for high-efficiency large-area OPV devices. Spatially regulated QDs are highly valuable emitters for light-emitting applications. We aim to show that cooperative spatio-temporal regulation of nanomaterils is of vital importance to the development of functional devices.

Investigation of pH-dependent photophysical properties of quantum nanocrystals by fluorescence correlation spectroscopy

Quantum dot (QD) and quantum rod (QR) nanocrystals are widely used non-organic nanocrystals. Their strong fluorescence and photostability make them suitable for biomedical imaging applications. However, their pH-dependence and antibunching properties have not been studied much, especially in aqueous conditions. In this report, we used fluorescence correlation spectroscopy (FCS) with high temporal resolution to demonstrate that the fluorescent blinking and antibunching of QDs/QRs can be changed by varying the pH of their solutions. Furthermore, herein, we reported the relationship between the aggregation and antibunching relaxation time of QDs/QRs for the first time. The findings of this study suggest that FCS can be used to discover novel environmental indicators via observing nanosecond and microsecond phenomena.

Grafted c-kit+/SSEA1- eye-wall progenitor cells delay retinal degeneration in mice by regulating neural plasticity and forming new graft-to-host synapses.

BackgroundDespite diverse pathogenesis, the common pathological change observed in age-related macular degeneration and in most hereditary retinal degeneration (RD) diseases is photoreceptor loss. Photoreceptor replacement by cell transplantation may be a feasible treatment for RD. The major obstacles to clinical translation of stem cell-based cell therapy in RD remain the difficulty of obtaining sufficient quantities of appropriate and safe donor cells and the poor integration of grafted stem cell-derived photoreceptors into the remaining retinal circuitry.MethodsEye-wall c-kit+/stage-specific embryonic antigen 1 (SSEA1)− cells were isolated via fluorescence-activated cell sorting, and their self-renewal and differentiation potential were detected by immunochemistry and flow cytometry in vitro. After labeling with quantum nanocrystal dots and transplantation into the subretinal space of rd1 RD mice, differentiation and synapse formation by daughter cells of the eye-wall c-kit+/SSEA1− cells were evaluated by immunochemistry and western blotting. Morphological changes of the inner retina of rd1 mice after cell transplantation were demonstrated by immunochemistry. Retinal function of rd1 mice that received cell grafts was tested via flash electroretinograms and the light/dark transition test.ResultsEye-wall c-kit+/SSEA1− cells were self-renewing and clonogenic, and they retained their proliferative potential through more than 20 passages. Additionally, eye-wall c-kit+/SSEA1− cells were capable of differentiating into multiple retinal cell types including photoreceptors, bipolar cells, horizontal cells, amacrine cells, Müller cells, and retinal pigment epithelium cells and of transdifferentiating into smooth muscle cells and endothelial cells in vitro. The levels of synaptophysin and postsynaptic density-95 in the retinas of eye-wall c-kit+/SSEA1− cell-transplanted rd1 mice were significantly increased at 4 weeks post transplantation. The c-kit+/SSEA1− cells were capable of differentiating into functional photoreceptors that formed new synaptic connections with recipient retinas in rd1 mice. Transplantation also partially corrected the abnormalities of inner retina of rd1 mice. At 4 and 8 weeks post transplantation, the rd1 mice that received c-kit+/SSEA1− cells showed significant increases in a-wave and b-wave amplitude and the percentage of time spent in the dark area.ConclusionsGrafted c-kit+/SSEA1− cells restored the retinal function of rd1 mice via regulating neural plasticity and forming new graft-to-host synapses.Electronic supplementary materialThe online version of this article (doi:10.1186/s13287-016-0451-8) contains supplementary material, which is available to authorized users.

Application of Quantum Dots in Biological Detection

During the past ten years,the application of semiconductor nanocrystal material-quantum dots has displayed an increased tendency in scientific and industrial production fields,and a broad research is developed from materials science to biological applications. The application of quantum dots has substantially impacted on many research areas,such as biological imaging,phototherapy,drug / gene delivery,and solar cell. It is a key point to control the interactions between quantum dots and cell through adjusting surface properties of quantum dots. As the potential cytotoxicity of quantum dots arise,nanotoxicity becomes an important indicator of nanomaterials security assessment,and scientists pay more attention to the research of their potential toxicity. In this review we overviewed the properties of quantum dots,the applications in cell biology and the cytotoxicity research in biomedicine related field. Moreover, the future prospects for applications of quantum dots were briefly presented.

Quantifying Colonization Potential of EnterohemorrhagicEscherichia coliO157 Using BovineIn VitroOrgan Culture and Immunofluorescent Staining

A robust semiquantitative method for measuring the colonization potential of O157 enterohemorrhagic Escherichia coli (EHEC) strains was developed combining an established ex vivo model infection system, bovine in vitro organ culture, with detection of bacteria attached to tissue sections by immunofluorescent assay (bIVOC-IFA) using Quantum dot(®) nanocrystal technology. The method was tested on ten O157 strains chosen to reflect a diversity of genotypes found in New Zealand based on the novel polymerase chain reaction-binary typing (P-BIT) system. High- and low-colonizing EHEC O157 strains were identified using bIVOC-IFA, with the highest colonizing strain belonging to the pulsed-field gel electrophoresis type most commonly identified from New Zealand beef meat. Furthermore, all of the toxigenic O157 strains exhibiting a low-colonizing phenotype were closely related, belonging to the same P-BIT genotype cluster. Future use of this method to characterize EHEC strains could provide valuable information for risk assessment and risk management interventions aimed at improving food safety along the beef farm to fork continuum.

Evaluation of Quantum Confinement Effect in Nanocrystal Si Dot Layer by Raman Spectroscopy

Quantum confinement effect in the nanocrystal-Si (nc-Si) was evaluated by Raman spectroscopy. The nc-Si dot layers were fabricated by the H2 plasma treatment for the nucleation site formation followed by the SiH4 irradiation for the nc-Si growth. Post-oxidation annealing was also performed to improve the crystalline quality. After post-oxidation annealing for 5 or 10 min, the asymmetric broadening on the lower frequency sides in Raman spectra were obtained, which can be attributed to the phonon confinement effect in nc-Si. Furthermore we confirmed that hydrostatic stress of approximately 500 MPa was induced in nc-Si after post-oxidation annealing.

Evaluation of Optical Properties for Nanocrystal Si Dot Layers Fabricated by CVD as a Function of Size Reduction

Raman spectroscopy and photoluminescence were performed in order to understand the optical properties of nanocrystal Si in relation to quantum confinement effects. The nanocrystal Si (nc-Si) dots in the SiO2 layer were fabricated by the H2 plasma treatment and chemical vapour deposition followed by the oxidation of the nc-Si dots surface. The post-annealing was also performed to improve the crystalline quality of nc-Si at 1050 °C for 5 and 10 min. There is a good correlation of the quantum confinement effects between the results of Raman spectroscopy and photoluminescence. The Raman spectra from nc-Si were analysed using the model of Richter et al. As a result, the sizes of the nc-Si dots were consistent with those obtained by transmission electron microscopy and X-ray diffraction. Moreover, the compressive stress in the nc-Si dots were evaluated which was induced by the SiO2 surroundings.

Molecular Control of the Nanoscale: Effect of Phosphine–Chalcogenide Reactivity on CdS–CdSe Nanocrystal Composition and Morphology

We demonstrate molecular control of nanoscale composition, alloying, and morphology (aspect ratio) in CdS-CdSe nanocrystal dots and rods by modulating the chemical reactivity of phosphine-chalcogenide precursors. Specific molecular precursors studied were sulfides and selenides of triphenylphosphite (TPP), diphenylpropylphosphine (DPP), tributylphosphine (TBP), trioctylphosphine (TOP), and hexaethylphosphorustriamide (HPT). Computational (DFT), NMR ((31)P and (77)Se), and high-temperature crossover studies unambiguously confirm a chemical bonding interaction between phosphorus and chalcogen atoms in all precursors. Phosphine−chalcogenide precursor reactivity increases in the order: HPTE < TOPE < TBPE < DPPE <TPPE (E = S < Se). For a given phosphine, the selenide is always more reactive than the sulfide. CdS(1-x)Se(x) quantum dots were synthesized via single injection of a R(3)PS-R(3)PSe mixture to cadmium oleate at 250 °C. X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV/Vis and PL optical spectroscopy reveal that relative R(3)PS and R(3)PSe reactivity dictates CdS(1-x)Se(x) dot chalcogen content and the extent of radial alloying (alloys vs core/shells). CdS, CdSe, and CdS(1-x)Se(x) quantum rods were synthesized by injection of a single R(3)PE (E = S or Se) precursor or a R(3)PS-R(3)PSe mixture to cadmium-phosphonate at 320 or 250 °C. XRD and TEM reveal that the length-to-diameter aspect ratio of CdS and CdSe nanorods is inversely proportional to R(3)PE precursor reactivity. Purposely matching or mismatching R(3)PS-R(3)PSe precursor reactivity leads to CdS(1-x)Se(x) nanorods without or with axial composition gradients, respectively. We expect these observations will lead to scalable and highly predictable "bottom-up" programmed syntheses of finely heterostructured nanomaterials with well-defined architectures and properties that are tailored for precise applications [corrected].

COMPARATIVE ANALYSIS OF DIRECT FLUORESCENCE, ZENON LABELING, AND QUANTUM DOT NANOCRYSTAL TECHNOLOGY IN IMMUNOFLUORESCENCE STAINING

A comparative analysis was performed to determine the sensitivity and efficiency of three fluorescent labeling techniques, including direct fluorescent-antibody staining (FA), Zenon labeling, and quantum dot (QD) nanocrystal technology. Two varicella-zoster virus immunoglobin (Ig) G forms, mAb 4F9 and mAb g62, were selected for these studies. The results indicated that: (1) All three methods demonstrated similar brightness and photostability; (2) the time required to conjugate the antibody varied, with Zenon labeling being the quickest; and (3) the stability of each conjugated complex was different, with FITC/rhodamine-conjugated antibody being the most stable.

Synthesis and magnetic characterization of Pb1−xMnxS nanocrystals in glass matrix

The synthesis of manganese-doped PbS (Pb1−xMnxS) nanocrystal (NC) dots within a borosilicate glass matrix has been investigated by atomic force microscopy, electron paramagnetic resonance and magnetic measurements. The fusion method was employed in the preparation of the magnetic semiconductor NC dots whereas the measurements performed showed changes in the physical properties of the manganese-doped dots as a result of the Mn2+-incorporation into the hosting PbS crystal structure. Nevertheless, the data indicated that only a small fraction of the nominal Mn-doping was incorporated into the PbS NC dot, in both lower (0.5%) and higher (40%) nominal doping ends. For the lower nominal Mn-doping end (0.5%) we found only about 0.05% actually incorporated into the PbS NC dot whereas about 0.45% appeared dispersed throughout the glass template as isolated paramagnetic centres.

Shape Dependence of Resonant Energy Transfer between Semiconductor Nanocrystals

We theoretically study the energy transfer between semiconductor nanocrystal dots and rods of CdSe using a semiempirical pseudopotential method (SEPM) description of the electronic structure of the...

The effect of confinement on the electron thermal conductance of a nanocrystal

Coulomb blockade oscillations are found in the electron thermal conductance of a quantum dot (nanocrystal) in the regime of weak coupling with two electrode leads that is calculated within a linear response theory. An analytical expression is obtained in the quantum limit where electron level spacing is non-negligible. The effect of confinement on the electron thermal conductance is thereby explicitly shown. It is shown that in the quantum limit the periodicity of the Coulomb-blockade oscillations of the electron thermal conductance is the same as of the conductance. The shape and the magnitude of the electron thermal conductance depend explicitly on the temperature and the energy level spacing. It is found that the electron thermal conductance decreases nearly exponentially with increasing confinement and decreasing temperature.

Enhancing memory efficiency of Si nanocrystal floating gate memories with high-κ gate oxides

High-performance floating gate memory devices of Si nanocrystal (NC) dots on HfO2 gate oxide were fabricated at temperatures below 400°C. A large counterclockwise hysteresis of 5.2V, at an applied voltage of +6V, and a stored charge density of 6×1012cm−2 were observed. Moreover, the smaller band offset of the high-κ tunneling layer resulted in higher charge tunneling probabilities towards the Si NC dots than those observed with a SiO2 tunneling layer. Advantages in terms of scaling for a high-performance and stable reliability memory device are confirmed.

Effect of SiO2 Tunnel Oxide Thickness on Electron Tunneling Mechanism in Si Nanocrystal Dots Floating-Gate Memories

The effect of tunnel oxide thickness on the charging/discharging mechanism and data retention of Si nanocrystal dot floating-gate devices was studied. The key point here is the difference in tunnel oxide thickness. Other parameters that can affect memory properties were carefully controlled. The mechanism of electron discharging was discussed on the basis of the difference in tunnel SiO2 thickness. Direct tunneling was found to dominate in the 3- and 5-nm-thick SiO2 tunnel oxides. However, Fowler–Nordheim (FN) tunneling affects the electron discharging characteristics of a thicker SiO2 tunnel oxide. It was found that memory properties also strongly depend on tunnel oxide thickness.

Experimental investigation of tunnel oxide thickness on charge transport through Si nanocrystal dot floating gate memories

The effect of tunnel layer thicknesses on the charging/discharging mechanism and data retention of Si nanocrystal dot floating gate devices was studied. Floating gate memories of Si nanocrystals dots with three different SiO2 tunnel thicknesses were fabricated, the key variable being tunnel oxide thickness. Other parameters which can affect memory properties were carefully controlled. The mechanism of electron discharging is discussed based on differences in tunnel SiO2 thickness. Direct tunneling was found to predominate in the cases of 3- and 5-nm-thick SiO2 tunnel layers. However, Fowler-Nordheim tunneling affects the electron discharging characteristics with thicker SiO2 tunnel layers. Clear characteristics in discharging peak differences could be observed in capacitance-voltage measurements on metal-oxide semiconductors with Si floating nanodot devices. Memory properties also depended strongly on tunnel oxide thickness.